Currently the disposal of worn tyres from vehicles represents a considerable problem. These tyres are not readily disposable and, in their normal state, occupy a substantial space. If they are placed on or in land-fill sites this either creates an unsightly mound or occupies substantial underground land-fill capacity. There is also the risk of a fire hazard which can be difficult to control and usually results in the emission of toxic fumes. The destruction of tyres by burning is not environmentally acceptable on open sites due to the emission of toxic fumes. Burning of tyres in an incinerator consumes substantial energy and creates large quantities of unusable waste products, and requires sophisticated emission scrubbing device to remove toxins.
It is an object of this invention to provide a means of degrading tyres in a manner which is environmentally acceptable and which ideally will result in usable degradation products
According to the invention there is provided a degradation device suitable for degrading tyres and comprising an enclosed chamber providing an annular housing space for a tyre to be treated, a microwave generator connected to a wave guide for splitting the generated microwave energy into arms which are provided with outlets which will direct the energy both externally and internally of the annulus of the housing space, means for supplying an inert gas into the chamber, means for drawing off volatile gaseous products of the process, and collection means within the chamber for the solid degradation products created by operation of the device.
The arms could be constructed in accordance with electronically calculated design parameters to ensure suitable transmission of the microwaves so as to control xe2x80x9cExe2x80x9d and xe2x80x9cHxe2x80x9d plane microwave energy. Apparatus for controlling reflected energy in either plane could also be incorporated. There could additionally be apparatus, such as a magnetic induction system attached to the device to optimise the induction of microwave energy to the tyres by focusing the microwaves in juxtaposition to any metallic bracing contained in the tyre.
A device of this nature is particularly suited to degrading tyres by providing that both the external and internal surfaces of the tyre are bombarded with microwaves by the wave guide and ensuring that the device is able to operate, by introduction of an inert gas, in such a way that oxidation and oxidative combustion during the whole process are minimised or excluded. Suitable control systems for the microwaves, for the inert gas and for the chamber temperatures can be operated to adjust processing to exclude the formation of pyrolytic graphite specifically, and other unwanted degradation products, and also to improve production of desirable products and to adjust processing times.
Operation of a degradation process on a tyre within a device of this nature can produce usable by-products in the form of carbon, steel and various oils which can be separated out from a condensate of the exhausted gases. The mixture of non-condensable gases may have a usable potential calorific value dependent on the process control parameters.
Ideally the device will include a drive motor and support assembly enabling rotation of the enclosed chamber and/or the tyres independently of the chamber, with respect to the microwave standing wave pattern generated in the process chamber by the microwave generator. Additionally, and desirably the device will include a drive member and support assembly enabling reciprocation of the enclosed chamber and/or the tyres independently of the chamber, with respect to the microwave standing wave pattern generated in the process chamber by the microwave generator. Rotation and reciprocation of a tyre within the device, during degradation processing of the tyre, improves the efficiency of the system by minimising xe2x80x9cExe2x80x9d and xe2x80x9cHxe2x80x9d plane energy transfer inconsistencies and a fairly consistent degradation of the tyre can then be achieved
It is much preferred that a convective kinetic energy transfer (heating) mechanism should be provided in the walls of the primary processing chamber to minimise premature condensation of process-released gaseous products. A thermal insulation jacket can be added to minimise convective energy losses.
The wave guide can be designed such that one set of arms directs microwaves directly into the inner region of the annulus of the housing space and another set of arms directs microwaves generally around the outer region of the annulus of the housing space. Each set could comprise a single arm.
The device can be arranged to stand such that the chamber and the annular housing space are set horizontally, with the wave guide being directed generally vertically into the chamber. Alternatively the device can be arranged to stand with the chamber and the annular housing space set in any generally vertical plane, with the waveguides also set in any plane relative to the device, but ideally in a plane lying normal to the plane of the chamber.
An outer condensing sleeve can be provided around the chamber to facilitate primary condensation of volatile gases leaving the process chamber. A removal mechanism comprising sealable hopper doors opening to a screwfeed, moving belt or table assembly can be provided at the base of the process chamber for removing particulate degradation products. A magnetic device can be attached to the process chamber or to a removal mechanism to extract any ferrous metallic degradation products.
Ideally there will be a pump or other recycling device to draw gases from the chamber. A passageway leading to the recycling device will preferably then include a condenser for condensing volatile products out of the outlet gases from the chamber. A separator can then be provided for separating out condensed volatile products This device will ideally include a mechanism for containing, recycling and/or destroying gases from the non-condensible fraction, including a means whereby suitable component gases may be used in the inert gas system of the device.
A support is ideally provided for holding a tyre to be treated above electronically inactive parts of the process chamber. This support member can be cage-like and/or can incorporate a support web on which a tyre can be supported in the process. This support cage or web can be constructed in resonant length sections to optimise energy transfer or inductance of microwaves.
The invention further extends to a process of degrading a tyre utilising a degradation device of this invention as hereinbefore defined, wherein a tyre is located in the annular housing space within the chamber and is subjected to microwave radiation directed at the outer and inner surfaces of the tyre by the wave guide, whilst maintaining atmospheric conditions within the chamber, by utilization of inert gases, to limit the possibility of combustion or oxidation of degradation products created by the process, and by drawing off volatile products from the chamber as they are created, and collecting solid degradation products for recycling.
Preferably the atmosphere within the process chamber will be maintained at a level such that the oxygen level is kept below 10 to 12%, preferably at about 5 to 8%. Carbon monoxide, nitrogen or other essentially non-ionic gases may be used to suppress or maintain the oxygen content at the desired level. Advantageously carbon monoxide formed as a by-product of the process can be recycled into the chamber as an oxygen suppressant.
The operating temperature within the process chamber should be maintained at such a level as to prevent micro-environment overheating in the process; preferably the maximum operating temperature in the chamber should not exceed 350xc2x0 C.
It is preferred that volatile gases withdrawn from the chamber are passed through a condenser, where they can be separated into their constituent fractions; the hot uncondensed gases can be taken directly from the chamber to a conventional kinetic energy device (internal combustion or gas burner type) for energy extraction and/or conversion. It is preferable that such a device has a containment or recycling or cleaning device attached to the final emission route in order to exclude the possibility of unwanted emissions to atmosphere.
Tyres may be processed singly or in multiples, in whole or shredded form, within the chamber. The tyre, or collection of tyres, could be compressed axially and held in the compressed state within the chamber prior to starting up of the process.
A dielectric accelerator, such as a carbon particle by-product of a previous operation of the process, may, with advantage, be placed within the tyre to enhance the operation time and/or initiation of the process.